Level luffing jib crane



Dec. 18, 1951 I; KAY

LEVEL LUFFING JIB CRANE 2 SHEETS-SHEET 1 Filed April 50. 1947 Dec. 18,1951 KAY 2 2,579,262

LEVEL LUFFING JIB CRANE Filed April 30. 1947 v 2 SI-lEETS-Sl-IEET 2Patented Dec. 18, 1951 UNITED S E S IEIN T ZQZF'FICE 2,579,262 I ILEVELLUFFEN G JIB CRANE Ignatius Kay, Lon'den, England assignoi" tcv TheWellman Sinith Gwen Engineer ingllorpora- .tion Limited,..London,England,..a companyiof Great Britain "Application April 30, 1947;SerialNoi745,033 1 In Great B'ritainMay 3, 1946 1 Glaim.

lufiing jibcrane comprises a frame, a balanced jib with free ends and apivot intermediate such ends, connectingimeansbetween-the jib and theframe constraining the said .pivot to move .in .an arcuate path,furtherconnecting means between the jib and the frame constrainingapOiIltDILthB jib offset from its longitudinal axis tomove .in-a pathdirected substantially radially with respect to the said arcuatepath,the said paths .being such that the lufiing of the jib-producessubstantially horizontal movement of its centrelof gravity andsubstantially verticalmovementof its end remote from :the load,.a..pulley .at the saidjibend, a secondfipulley on theframesubstantially vertically beneath the first pulley and 1a hoistingrope passing. froma winding drum on the-frame over the second. andfirstlpulleysand;over:a;hoistingpulley at ithe'load-carryingzend of thejib. In

such a crane the hoisting ropepulls actingon the jib are arranged tohave anequal moment about the centre-ofigravity of thejib, the ratiobetween the length of the jib forward of thersaidcentre and.thelengthiofthe remainder of the jib being equal to the .ratio betweenthe 'number'of parts of hoisting rope at the rearjib-endand the :num-

vber of .parts of. the same. repeat the forward jib-end.

The connecting vmeans between the jib and frame compriseda;pair.of.links, each pivoted at one end-to'the frameand at the otherend :to the jib, so disposed that .if extended beyond their 'pivots onthe jib they wouldmeet onithe intersection of a transverse verticalplane. containing the centre of gravity of thejiband a horizontal planecontaining the rear i jib-end. The, upper link extended from a pointon'the. frame .horizontally opposite the centre of gravity of the jibtoa point-on the latter spacedzbothfromttherrear jib-end and fromtheicentre .of. gravity :by an amount equal to "the :length of thelinkywhereas the lower link extended froni anpoint Jon the frameverticallybeneath 'the'rear ijib-endi to :a

point on the jib offset downwards from'tthe point 'of attachment of theupper linkuto .the..;jib, the

distance-between the 'two. pivotsonthe jib being equal to the-lengthofthe upper link. fl' orepracticalreasons, thesaid upper 'link wasgenerally rebladbyan equivalent but siiorterilink having one end pivotedto the frame ;at;.a.point lying on a-l-ine joining the pivot on.the;jibfor the lower link-to the .point atwhich the frame-connected -end of theupper 'linkwouldlotherwisebe disposed. The shorter link extended incthedirection of the intersection point for the upper and lower links (whenextended) and was pivoted to the jib at a point lying on a line joiningthe jib-connected end of the lower link to the point at which the upperlink would otherwise be connected to the jib.

.Insuch cranes there is a point on the jib (referred to hereinaftenasthe reference point) -which:subdivides the length .-of the jib into twoparts, a head portion and aitail portion, the lengths ,of which bear thesamerelationship to each other asthe number of parts of the hoistingropeat the tail of the jib :bears-to the ,numberlof 'parts of .thesamerepeat thehead ,of .the jib. Hence, if there is .one -.part of ropeatboth the head ,and the tail of .the jib, the reference point is(located mid-way of the length of the jib, whereas if thereisone partof-ropeat the head and three parts at the tail, the reference point. islocated at one quarter of the lengthof the jib from the tailsendthereof.The referencepoint in the cranes accordingto thesaid earlier inventionhas :been constrained to ,move horizontally during the lufiing' of thejib .(by reason of the linkage arrangements describedland it has there-.fore been considered essential ,toarrange that the centre'of gravity ofthe jibshouldcoincidewith the said reference point, as will have becomeclear from qtheabove brief descriptionsof the earlier in- :vention. Thepathof travelof the reference point .being horizontal, .the rearjib-end-was necessarily arranged to move vertically and thepartorparts.of hoisting rope-extending from the, pulley at this end to that on thecrane frame was .or werealso vertically directed.

Now it frequently happens that the. ,practical requirements-in theconstruction. of alevel lufling gjib crane make. it inconvenient eithertoarrange the centre of gravity ofztheljib to-coincide with thereference pointer. to ,arrangethe pulleyon the-crane frame verticallybeneath that on .the rear jib-end. Forie x-ample, in theearlier specificationtof United States Patent No. 2,386,475 there is shownandrdescribed -a construction having the reference-;poi11t;located:mid-way-of the length? of the jib. .;Ina practical construction this:.would entail counterweighting, the forward; end of J the. jib tor ,2employing ,-Il ight-;metal inthe -..con- -.str.uction;'of therear-end-of the jib,.or the-useof both expedients, in orderrto causethe' centraof gravity of the jib to coincide with the reference point.

The object of the present invention is to provide modifications in thesaid earlier invention which shall enable'the effect of non-coincidenceof the centre of gravity of the jib and the reference point to beovercome without such use of forward counterpoise or other undesirableexpedient.

According to the invention, in a level lufiing jib crane substantiallyin accordance with the invention claimed in the said earlierspecification but having the centre of gravity of the jib disposedrearward of the reference point, the hoisting rope pulley at thetail-end of the jib is disposed so that a line joining the axis of thepulley to the reference point is canted upwards with relation to theline joining the reference point to the axis of the hoisting rope pulleyat the head of the jib through a predetermined angle a, and theconnecting means between the crane frame and the jib are arranged tocause the reference point to travel along a path inclined upwards andrearwards to the horizontal at an angle which is equal to where n is thenumber of parts of hoisting rope at the head of the jib and n1 is thenumber of parts of the hoising rope at the tail of the jib, so that thepulley at the tail-end will move along a path inclined downwards andrearwards to the vertical at the angle a and passing through the axis ofa hoisting rope pulley mounted on the crane frame, the centre of gravityof the jib thereby being constrained to move horizontally.

The nature of the invention will be more clearly understood from thefollowing description of some examples of the way in which it may becarried into eifect and the theoretical considerations which apply,reference being made to the accompanying drawings which are mainlydiagrammatic.

Fig. l is a line diagram illustrating the linkage arrangement whichconstitutes the main feature of the earlier invention referred to aboveand which is fully described in the specification of United StatesPatent No. 2,386,47 5,

Fig. 2 is a similar line diagram illustrating the modified arrangementof the present invention,

Fig. 3 is a diagrammatic side elevation of one form of crane embodying apractical example of the linkage arrangement shown in Fig. 2, therebeing one part of hoisting rope at the head and tail of the jib, and

Fig. 4 is a similar view of another form of crane according to theinvention in which a different location of the reference point on thejib is necessitated by an alteration in the reeving of the ropes, therebeing one part of hoisting rope at the head of the jib and three partsof the same rope at the tail of the jib.

In Figs. 3 and 4 only the parts essential to a clear understanding ofthe present invention have been indicated, the main members of the jibbeing shown in heavy lines and the main members of the frame by doublelines. Many of the bracing members and other known constructionaldetails, including means permitting of slewing the crane or traversingit along rails when desired, have not been illustrated as theirarrangement or construction will beobvious to those skilled in the art.

Referring first to the construction forming the subject-matter of theearlier United States Patent No. 2,386,475, shown in Fig. 1, a pivotedjib A, B (represented by its longitudinal centre-line) is suspended froma crane frame (not shown) by a pair of links, the pivotal point of thejib being at C. A downwardly extending arm D is rigidly fixed to the jibat the point C, is equal in length to the tail portion C2 of the jib,and has its lower end pivoted at E to the forward end of a thrust link Fwhich has its rear end pivoted at C on the crane frame verticallybeneath the end 2 of the tail portionCZ. A second link H is pivoted atits upper end on the crane frame at a point J vertically above the tailend Z of the jib, is of a length equal to that of the arm D and ispivoted at its lower end to the jib at the point C. The links F and H,when extended, meet at the point K which during the movement isconstantly vertically beneath a reference point L on the jib. Thehoisting rope pulls acting on the jib A, B, are represented by, thearrows M and N. The reference point is spaced from C by a distance equalto CZ and subdivides the jib into the head portion A and tail portion B.Due to the fact that the lengths of CZ, CL and CJ are all equal theangle ZJL is a right angle and the point J is horizontally opposite tothe point L.

It has been demonstrated in the earlier specification referred to thatluffing of the jib A, B, when thus supported from the crane frame,results in the reference point L always moving in a horizontal path, thetail end of the jib always moving in a vertical path, and the reductionor increase in the distance between the tail end of the jib and thepoint G always bearing a definite ratio to the lift or fall of the headend of the jib. The numerical value of this ratio depends on therelation between the lengths of the head and tail portions, A and B,respectively, of the jib and this relation is the same as that betweenthe number of parts of hoisting rope at the tail of the jib and thenumber of parts of this rope at the head of the jib. With the center ofgravity of the jib arranged to coincide with the reference point L andwith the hoisting rope pulls, M and N, arranged to have an equal momentabout the same point, the jib is in balance for any position of thepoint L along its horizontal path of travel. Moreover, the loadsupported from the head end of the jib A, B, will travel in a horizontalpath during lufling of the jib, provided that the hoisting rope at thetail end of the jib runs vertically downwards to a pulley mounted on thecrane frame at or near to the pivot G.

For practical constructional reasons it is preferred to replace the linkH by an equivalent link 0, this being pivoted on the crane frame at apoint P lying on a line EJ and pivoted on the arm D at a point Q lyingon a line PK. The link H is removed when the link 0 is fitted.

As has been indicated above, it has heretofore been considered essentialto arrange that the centre of gravity of the jib A, B, should coincidewith the reference point L, and the part or parts of the hoisting ropeextending from the tail end of the jib to the pulley on the crane framewas or were necessarily directed vertically. The rectangle JLKZ thus hadits sides LK and JZ disposed vertically.

According to the present invention, the limitations and disadvantages ofthe earlier. linkage arrangement may be removed by making somemodifications therein, as shown in Fig. 2. In this .figure, parts orpoints corresponding to thoseof Fi r are-indicatedby the'same fferenoecharacters ashave been used i describing Fig The example chosen*has" thereferencepoint L disposed mid-way of the 1efigtn-or the ji-bA, B, (thelin'eB (or-LY) representingthe normal position-of the tail portion) andthe centre or gravity'CG ofthe jib is disp'o'sedrearward of thereference-point L. If the diagonalLZ (of-the rectangle ULKZ)passingthroughthe centre" of gravity CG were to coincidewith thecontinua- "tion B of the upper'part of the jib as in-tlie'con-*struction of Fig. L-lufiing of thisjibwould'cause the centre of"gravity CG to 'rise' and'fa-ll as the "point L travelled horizontally.This is preverited with the "construction-of- FigrZ-in'which thereference-point L is arranged to move along-apath 'LJ that isinclinedupwards andrearwards with respectto the horizontal at an angle18 such-that the" centre of gravity CG will always move along -ahorizontal pah. The'value of the angle ,8 is readily determinedbyplotting the extreme positions of the jib (assuming horizontal movementof the reference point L) --measuring the fall of the centre-of-gravity- CG from the one 'positionto the other, andthenarrahging-for the reference point -L to rise by acorrespondingamount 'for the same displacement of the jib. The-angle 3 is generallyabout-8 -for cases'where the reference pointL-is -at the centre oflength of the jib. Due to the inclination of the path LJ' the rectangle-JLKZ which fixes the positions of the points K andJ-is swung about itscorner L through the angle 15. The pivotal-point C of the jib is nowdisposed on the' 'second diagonal LZ of the rectangle (JKbei-ng thefirst'diagonal) and this diagonal LZ inclines upwards with relation tothe continuation-B of the centre-line of the upper partofthejib, --atananglefi. --The geometrical construction determining the positions andlengths of the links and- F and of the arm-Dis otherwise the-sameasinFig. 1, the link D being shown as terminating at the'line B forconvenience but obviously being of the efizective length EC.

Again due to the inclination-0f the path LJ,

the rear jib-end no longer-moves vertically nor does' its extent-oftravel bear the constant defi- "n'ite'relationship to the rise and fallof the head "of-the-jib which is necessary to secure level lufilng ofthe load. In order to secure this action, therefore, the hoisting ropepulley which would normally be disposed at the point Y on the tailportion of the jib is raised above the said point to an extent suchthata line -B joining its axis X to-the reference point Lmakes an angle(7. with the continuation B of the upper part of the centre line and isof the same length as said line B. The-pulley now travels along a path(the disposition of which is shown by arrow N) also making an angle a.with the vertical, as the jib is luffed. It can be demonstrated that thedis- 'tance h"travell'ed by the "pulley albn'g'thisp'ath always bears adesired constdhfileitibns'liip"to the verticaldistance-h -through whichthe head of the 'jib is displaced at the same time. For the exampleillustrated the; distances h and'h are equal, as the nurnber of parts ofhoisting rope at the head and the tail of the jib are also the same.

="given by the expression where n is the number of parts of rope at theangle" {3 is three qnarters' of the angle a.

"jib at the position or -ma xim'u'm -rea'ch is then decided andtheposition rormimmum reach is "also selected. j

The jibis then drawn in -its'=two and positions movewverucany.The'vertical fall 'in the positidnbf the centreof'fg'ravity-in -themovelnent "from" the one positionto' the' other' is thn'ineas- "ured'andthe line *joining the' two-locations of L "is inclined upwards to thehorizontal *from the maximum reach position of L at an'angle "fl su'chthat n at the minim m-reach position wi u have risen vertically through-the same distance as the'centre of gravity fell. A-n anglewiis thencalculated'from "and the tail pdi'tion'foff the .jiaextenamg'irrom thereference point L? is ineimedtpwardsat this angle 'a with res ect to'ltshii'g'inal position. In

addition, the puneypn' thecrane frame ispfo'sihoned on'a linemak'ing"an'angle d'with" the vertical] from the friew position "of the A tail'Iid of'the jib. V

The "rectangle J ISKZ' is then constructed with the side JL'atanangle 8to the horizontal and 'ql'lal in length to the" product 6f the length ofthe tailend 0f the jib and' th (B'O'Sine'Of trieangle 0. The'side LK'is'inade equar to the"pr'odilctof the length of the tail end of "the "j iband the 'sine' of the angle 0. The intersection "of the'diago'nals ofthe rectangle fixes "the position "of the point C, "and the appropriateposition for the point C for thefiosition or the jib in ithe minimumreach setting is also determined'by 'dr'alwing'the 'jibtiiith thediagonal LZ in the correctrelativ'e position Strikingan 81rd from ectLZ'at C1. Arcs J with arafdiiis to are struck from c andbfwi'tha'ra'dius 'J'Gand their intersection fixes" the position "of" the pointE. KEfiiroducedgivesthe "dir'eiition of the link position of-Q iscnos'enon EC ('gen'erallyas the result ofp'ractical ex erience) so that'KQ 'p'ro- I diled 'will intersect J E E at P appropriatel close to thegeneralpositioii ofthe'ta'ilbf' the "j ib"wh"e'n The positionsandler'igthsbf thearm Derid the linksFand O are "now fixed to give"the"co'rrect motion "of the will move in the direction N.

A"practieairorm oftonstructmn of a crane corresponding to the diagram"of Fig. '2 is illus- 'trated by" Fig. 3. Here thebraneframeisindiplatform X" which'h'iayhe driven in any suitable "manner forsl'eWing-the'ora fie and may in turn be mounted on rails inamanner,peimitting of the crane being displaodhodlly. The parts of thecrane which correspond to the elements of the diagram of Fig. 2 areindicated by the reference characters also used in that diagram. Only.to the frame.

the main outer members of the jib have been shown in heavy lines, thebracing members and other known constructional parts being omitted forclaritys sake. Additionally illustrated are a pulley R at the head ofthe jib, a pulley S at the tail-end of the jib, a load hook T, a run Uof the hoisting rope extending from the pulley U on the crane frame (towhich the part N of the rope passes from the pulley S) to the windingdrum V, and lumng gear comprising a screw Y" pivotally attached at Y tothe link and engaged in a motor-driven nut Z which is pivotally mountedat Z on the crane frame W.

In operation, the jib is luffed by rotation of the nut Z". The screw Y"passes through the nut Z and thus draws the link 0 towards the pivot Z.Since the point P is fixed on the frame, the movement of the link 0towards the pivot Z produces arcuate movement of the free end of thelink 0. The jib-pivot Q is at this free end and is thus moved arcuatelywhen the nut Z is turned. The jib-pivot Q is rigidly connected to thearm D, which at its other end is pivoted at E to the forward end of athrust link F, which in turn is pivoted at its rear end G Thus the pivotE- is constrained to move on an arcuate path having its centre at G.Since the link F is relatively long and the movement of the pivot Erelatively short, this arcuate path approximates to a straight linenormal to the link F, that is to say, along the line PE. The arcuatemovement of the jib-pivot Q and the movement of the pivot Eapproximately' along the line PE causes the arm D to pivot about E in ananticlockwise direction. Since the arm D is rigidly connected to thejib, this will also pivot about E in an anticlockwise direction, so thatthe pulley R at the head of the jib will swing upwards and inwards.

Owing to the construction of the crane and as explainedin relation tothe diagram of Fig. 2, the reference point L will move upwardly andinwardly along a line lying at an angle ,8 to the horizontal, thetail-end of the jib will move downwardly towards the frame along a linelying at an angle a to the vertical, and the centre of gravity G willmove inwardly along a horizontal line.

Fig. 4 shows another construction in which, as far as possible,corresponding parts are again indicated by like reference characters.

In this case, the centre of gravity of the jib (not indicated) islocated somewhat lower down the jib than the reference point L which isitself at a distance from the pulley S of one-quarter of the length ofthe jib A, B, suitable counterweighting being resorted to, as will beunderstood, but the counter-poise (not shown) being arranged on thecanted up tail-end of the jib. Hence a single part M of the hoistingrope at the upper end R. of the jib requires three parts of the samerope at the lower end S of the jib, and this is ensured by suitablyreeving the rope, as shown at N before it passes at U to the drum V. Theoperation of this crane is substantially as already described above,each of the three parts of rope N releasing or taking up one third ofthe total rope required when the jib is luffed.

.It is to be understood that the theoretically correct arrangementaccording to this invention is, as stated above, with the centre ofgravity located on the diagonal LZ of the rectangle JLKZ but in practicesome slight departure from this condition is sometimes unavoidable dueto manufacturing difficulties.

What I claim is:

A level luffing jib crane comprising a supporting frame, a balanced jib,a hoisting pulley at the load-carrying end of the jib, a firstcounterloading pulley at the end of the jib remote from the loadcarrying end and so disposed that a line joining its axis to a pointalong the length of the jib located between the centre of gravity of thelatter and the hoisting pulley is canted upwards through a predeterminedangle a. with relation to a line joining the said point to the axis ofthe said hoisting pulley, a pivot for the jib located between the saidends thereof, a second counter-loading pulley so located on thesupporting frame beneath and rearwards of the first counter-loadingpulley that a line joining the axes of the counter-loading pulleys willmake the angle a. with the vertical, a winding drum on the said frame, ahoisting rope passed over said hoisting pulley and over said first andsecond counter-loading pulleys and attached to the said winding drum,the number n of parts of the said rope at the load-carrying end of thejib bearing the same ratio to the number m of parts of the said rope atthe other end of the jib as the distance between the said point of thejib and the said other end bears to the distance between the said pointand the load-carrying end of the jib, means mounting the jib-pivot onthe said frame for arcuate movement about a point thereon, a rigid parton the jib extending at an angle downwards away from the longitudinalaxis ,of the jib with its upper end proximate to the jib-pivot and itslower end spaced from the said jib-pivot by approximately the distancebetween the latter and the first counter-loading pulley, meansconnecting the lower end of the said jib-part to the frame for movementsubstantially along a line joining the said lower end and the point onthe frame about which the jib-pivot moves, and means for luifing the jiband thereby simultaneously producing displacement of both the jib-pivotand the lower end of the said jib-part so that the said point in thelength of the jib moves along a path inclined upwards and rearwards tothe horizontal at an angle 13 which is equal to n-l-m and the firstcounter-loading pulley moves along the line joining the axes of the twocounterloading pulleys, the centre of gravity of the jib thereby beingconstrained to move horizontally.

IGNATIUS KAY.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,036,386 Andersen Apr. 7, 19362,386,475 Kay Oct. 9, 1945 FOREIGN PATENTS Number Country Date 500,459Germany June 21, 1930

